<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        .box{
            height: 600px;
            width: 80%;
            min-width: 800px;
            background-color: skyblue;
            margin: auto;
        }

        .left,.right{
            float: left;
            width: 200px;
            height: 100%;
            background-color: aquamarine;
        }
        
        .left{
            margin-left: -100%;
        }

        .right{
            margin-left: -200px;
        }

        .center{
            float: left;
            width: 100%;
            height: 100%;
            background-color: wheat;
        }

        .inner{
            margin: 0 200px;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="center">
            <div class="inner">123</div>
        </div>
        <div class="left">123</div>
        <div class="right">123</div>
    </div>
</body>

</html>